OFFSET
0,6
FORMULA
a(n)= -2 + 2*Sum_{k=0..n} {[8*(sin(2*Pi*k/5))^2-5]^2-5}/20, with n>=0. a(n)= -2 + 2*Sum_{k=0..n} 1/50*{-9*[k mod 5]+[(k+1) mod 5]+[(k+2) mod 5]+[(k+3) mod 5]+11*[(k+4) mod 5]}, with n>=0.
a(n)=-2+2*Sum{k=0..n}{1-(k^4 mod 5)}, with n>=0 [From Paolo P. Lava, Feb 17 2010]
MAPLE
P:=proc(n) local i, j, k; for i from 0 by 1 to n do j:=-2+2*sum('(8*(sin(2*Pi*k/5))^2-5)^2-5', 'k'=0..i)/20; print(j); od; end: P(100);
MATHEMATICA
Table[#, 5]&/@(2*Range[0, 15])//Flatten (* Harvey P. Dale, Sep 11 2016 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, May 31 2007
STATUS
approved